1. Field of Invention
The present invention relates to a liquid crystal display (LCD), and more particularly, to an LCD in which a wire grid polarizer is formed on at least one of a thin film transistor substrate and a color filter substrate.
2. Description of the Prior Art
A liquid crystal display (LCD) comprises a thin film transistor (TFT) substrate with a pixel electrode formed thereon, a color filter substrate with a common electrode formed thereon, and a liquid crystal layer interposed between the two substrates. The LCD displays an image in such a manner that liquid crystal molecules are rearranged by applying a data voltage between the pixel and common electrodes to vary the amount of light transmitted through the liquid crystal layer. Since such an LCD is not self-luminescent, an image is displayed by means of light incident from the outside. To this end, a backlight unit is mounted to a rear surface of the LCD.
Light radiated from the backlight unit is not incident directly onto an LCD panel but incident with a polarization characteristic provided through a polarizer. Thus, an LCD displays an image using the optical anisotropy of liquid crystal molecules and the polarization characteristic of a polarizer.
An existing method of mounting a polarizer on an LCD panel includes attaching a polymer-type polarizer to the outside of an LCD panel. In a representative method, iodine molecules are chemically bonded on a polyvinylalcohol (PVA) base film in a predetermined direction through a wet stretching method to impart the polarization characteristic. While such a polarizer has a superior polarization characteristic, its manufacture requires an additional process besides those involved in manufacturing the LCD thereby increasing manufacturing cost.
Further, the existing attachable polarizer cannot provide polarization for each pixel of an LCD panel because the polarization characteristic are obtained by chemically bonding iodine molecules on the polyvinylalcohol (PVA) base film in a predetermined direction through wet stretching—resulting in the iodine molecules having a directional property throughout the entire film. Thus, polarization cannot be individually provided for each pixel of an LCD.
Further, since an attachable polarizer requires the use of an adhesive agent, the thickness of the LCD panel is increased due to the thicknesses of the adhesive agent.
Unlike the aforementioned polymer type polarizer, a small-sized wire grid polarizer has been developed and applied to products such as projectors. In the wire grid polarizer, a stripe pattern with a line width and interval smaller than the wavelength of red, green or blue light is formed on a base substrate. The wire grid polarizer is formed of a metal such as Al through a thin film machining method. That is, a wire grid polarizing pattern is formed with a line width and interval of 50 to 200 nm smaller than the blue light region that is the minimum optical wavelength of visual light. In an LCD, light incident on the wire grid polarizing pattern formed in such a manner from a backlight unit, the light advances while vibrating in horizontal and vertical directions with respect to its direction of advance. For this reason, only the light incident while vibrating in parallel with the spaces between regions in which the wire grid polarizing pattern is formed passes through. A wire grid polarizer is a structure in which the metal-based wire grid polarizing pattern is formed in such a manner.
If such a wire grid polarizer is formed of a metallic material such as Al with optically high reflectivity, the light incident from a backlight unit while vibrating in a vertical direction with respect to the spaces between the regions in which the wire grid polarizing pattern is formed does not pass through and is reflected back to the backlight unit. Thus, if a phase transition layer with reflectivity different from the wire grid polarizer, e.g., an anti-reflective layer, is formed under the wire grid polarizer, a phase shift occurs in the phase transition layer and the light is again incident to the wire grid polarizer, whereby an additional polarization occurs.
The wire grid polarizer has the same effect as a dual brightness enhancement film (DBEF) in which light recycling described above continuously occurs, so that polarization transmittance is enhanced. Since the light recycling can be obtained without using the complicated DBEF but by using a simple anti-reflective structure, a low-priced polarizer with high polarization can be manufactured.
However, the wire grid polarizer should be attached to the outside of an LCD panel like the existing polymer type polarizer after being manufactured through an additional manufacturing process. Therefore, such a wire grid polarizer is more expensive than a film attachable polarizer in view of costs and the number of the entire processes.